Champions in making top sales (8)
I believe the answer is:
apostles
'champions' is the definition.
(apostle is a kind of champion)
'making top sales' is the wordplay.
'making' indicates an anagram.
'top'+'sales'='topsales'
'topsales' is an anagram of 'APOSTLES'.
'in' is the link.
(Other definitions for apostles that I've seen before include "Christ sent twelve of them to preach the gospel" , "Followers or faith teachers - the Gospels name 12" , "Early Christians" , "Evangelists" , "Disciples chosen by Jesus" .)